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[note: click the “DOWNLOAD” button to the right to download the free config files for this interactive lab]

Transcript: Welcome to this CCDA lab where I’ll be looking at a case study of proper IP addressing design. We’ll also see how hierarchy in IP addressing supports summarization of routes.

So in this lab set up we have a couple of routers and you’ll notice there’s region, so this is the Africa region, connected to the HQ. Now the HQ could also be connected to together regions like say Europe, Asia, but in this lab we’ll only focusing on the Africa region.

Now, you’ll notice that all the IP addresses in the Africa region are ordered 10.0.0.0/12 block. So, that’s the block that has been assigned to the Africa region. Now, under Africa we have two countries, we have Nigeria and we have Rwanda. Now, Nigeria has been assigned a 10.1.0.0/16 block while Rwanda has been assigned 10.2.0.0/16 block.

Now, inside Africa, so the link between the countries, why isn’t 10.0.0.0/16. So for the links between the countries. In Nigeria, we’re using 10.1.0 for the links, so 10.1.0 here, 10.1.0 here. For the links between the cities, and then Lagos, Lagos has been assigned 10.1.1, right? Abuja has been assigned 10.1.2. Kigali, or between Rwanda and Kigali you have, between Rwanda_hub and Kigali you have 10.2.0.0/30, so we’re using 2.0 for links between the hub, as Rwanda_hub and other cities and inside Kigali you have 10.2.1, right?

So this is a very good hierarchy. It will probably be very difficult to achieve it in an already existing organization, but if you had a chance to develop or to implement of design a network from the ground up, then this is a good IP address instructor to use, right? Now between the HQ we have 10.253.0.0. So, EIGRP is running on this network, so if we were to go to the HQ, let’s take a look at …

Show IP route. Alright. So let me just increase this. Okay. So you notice EIGRP’s running, so this guys knows about every other person on the network. So you have the 10.0, this is between Africa and its countries, then this is inside Nigeria, and this is inside Rwanda. If I come to the Africa_hub, the same thing, so let’s enlarge this also, show IP route. Right, so, it knows about, everybody knows about everybody.

Now, this route here, 10.253.1.0 is in the hub. Right. So the hub is the one that owns that, so show IP interface brief. That’s this guy right here. Okay. Now Lagos also knows about everybody. Right, so show IP route. And then that’s what we have here. So everybody knows about everybody. See, if I try to ping 10.253.1.1, I can ping that, if I try to ping from Lagos, let’s say I want to ping Kigali, see, 1.1, I can also ping that, right? So everything is fine.

But if you look at it, is everything really fine? Since we’re using hierarchy then we can also as well just use summarization. But before we do that, let’s look at what happens when, say in Lagos, so if I do a show IP interface brief, the Lubbock interface is what we’re using as our 10.1. So if I were to bring down that interface, what do you think would happen?

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That’s network that went down would be broadcasted to every other person on the network. So let’s see that. Let’s go to simulation, the field type is just going to be EIGRP, right? And then, come back to Lagos’ router, and then say shut. Now, it’s ready to send that packet. So watch what happens, I’m just going to press capture forward. Alright, so it gets to Nigeria, Nigeria acknowledges it, wants to send it back at to Abuja, to Africa, does that. Africa will acknowledge it, send it Rwanda, can you see that?

So, if I actually click on one of them, you notice that it’s all about the 10.1 network that went down. So let me look for one. So let’s see, Nigeria. I need a packet that shows me like about the ten, okay so that’s that one. So it’s about, its query for the 10.1.1.0 network that went down. Let me just keep going, capture. Capture, as you can see, that’s a lot of packet because one network went down. And now, we are done. When I counted it, it was about, say four to six packets that was transmitted because this guy went down.

Now, networks fluctuate all the time, so it imagine if we are sending four to six packets for a network that goes down, comes back up, in a very large network. That is not good, right? That’s one of the reasons you need to use summarization.

So I’m going to show you the same lag but with summarization configured. So let’s go to six two. As again, see, it’s the same lab, but this time I have configured summarizations. So for example, if I got to Nigeria_hub, and I do a show run. So look at this, so on its interface to Africa_hub, it’s summarizing the 10.1 network. So that’s the network that it has, it’s summarizing that, and then, these guys, if you think about it, these guys only have one link to Nigeria_hub, they don’t need to know about every other person, they just need default route, right?

So it’s also sending a default route to the cities, right? So that’s what you have there. And Africa is also doing this same thing. So, if we do a show run, you notice that Africa is sending the 10.0/12 block, that’s what it’s summarizing to the HQ and it’s also sending a default route to the countries, right? Good.

So now let’s take a look at what happens to the routing tables. So if I do a show IP route. Now, all we are going to see is the default routes that the Nigeria_hub is sending to it. That’s all you need, right? Now if I come to the Nigeria_hub, show IP route, it’s going to know about the, that’s the Lagos, and then the Abuja, and then it’s going to have a default route to everywhere else, right? All the way up. So if I come to the HQ, this is one that is really nice. So if you come to the HQ, show IP route, can you see that the HQ has only one EIGRP route. So that’s the block here. So 10.0.12. This is a summary route I’m sending out.

So that’s all he knows about, it doesn’t need to know about the internal structure of the Africa_hub, really it only has one link and it can only get there through the Africa_hub, right? Cool. And we still have connectivity. So if I want to ping 10.253.1.1 I can still that ping that, and if I ping 2.1.1, I can still ping that, right? But something that we’ll see now, if I were to shut down that interface again, so I’ll go back to my simulation mode, and Lagos, and say shut.

Now watch what happens. The EIGRP packet is queued, capture forward, it sends it to Nigeria, Nigeria will send it to both Abuja and Africa, but that’s where it’s going to stop. That’s all. Yeah?

So now we’re done. Now compared to the four to six that we had, this one is about half the size of that, right? Now imagine if it was like a really big network. Then it’s going to be more gain or more value there, going to get from that, yeah? So summarization helps us in so many ways, and that’s one of things that we just saw. So instead of Africa_hub also asking HQ do you know about this, and Africa_hub asking Rwanda, they are all just going to say no, I know about that, and they talk only through you. So, I don’t know where 10.1.1.1 is, right?

So summarization is very helpful, not only does it reduce the size of your routing tables, it also makes your network more efficient.

Adeolu Owokade is a technology lover who has always been intrigued by Security. He has multiple years of experience in the design, implementation and support of network and security technologies. He's a CCIE (Security) with a new found love in writing.

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